Process of manufacturing n-methyl p-amino phenol.



ED STATES PATENT onmcn.

ROLLA N. HARGER, OF WASHINGTON, DISTRICT OF COLUMBIA.

No Drawing.

Specification of Letters Patent.

Patented Mar. 18, 1919.

Application filed December 10, 1918. Serial No. 266,117.

(DEDICATED TO THE PUBLIC.)

. claimed may be used by the Government of the United States, or any of its ofiicers or employees, inthe prosecution of work for the Government, or any person in the United States, without payment to me of any roya'lty thereon. This invention, if patented, is dedicated to the free use of the people of the United States of America.

This invention relates to a process of manufacturing N-methyl p-amino phenol, and the object thereof is to prepare this material in a more economical and efficient manner than the methods now in use. This material is a base and may be converted into the sulfate or other salts, and when converted into the sulfate its principal use is as a photographic developer.

I have discovered that N-methyl p-amino phenol may be manufactured by heating together in an autoclave hydroquinone and methylamin, the heating being carried out at temperatures ranging from 150 to 200 degrees for periods ranging from two to five hours. the heating period depending on the degree of temperature maintained, the longer heating period being required with the lower femperature and the-shorter heating periodwith the higher temperature.

I have also discovered that the reaction runsto greater completion when the methylamin is used in proportion'of about two equivalents of methylamin to one of hydroquinone and results in a much increased yield of the desired product.

The methylamin used in this process can be cheaply prepared by methylating ammonium chlorid by means of a 40% solution of formaldehyde as described by Brochet and Cambier (Bull.- Soc. Claim. (3), 13, 533) and later by Werner (J. Chem. Soc. 111, 844) and by Jones and Wheatley (Joma Amer. Chem. 800., 10, 1411) and subsequently liberating the free base with caustic soda or lime.

One of the former known methods of making N-methyl p-amino phenol, the sulfate of which is known commercially as metol, consists in heating together hydroquinone and methylamin, but the temperatures employed are much higher, and therefore, the pressure developed very much greater, and the time of heating from 3 to 10 times as long as by my process. The high pressures used in that process are thus seen to be replaced in my process by pressures practically one-tenth as great. In my process the pressure resulting, for instance, from the use of a temperature of 150 degrees is 120 lbs. per square inch, while in the former known method the pressures resulting from the use of the lowest temperatures preferred therein, which is 220 degrees, is about 600 lbs. per square inch, while the highest temperature recommended, which is 250 degrees, gives a pressure of over 1000 lbs. per square inch. It will thus be seen that my process permits the use of apparatus of ordinary construction, while the other requires specially constructed apparatus to withstand high pressures.

I conducted a numberof experiments in connection with the development of my process. The first experiments were carried out in a small steel autoclave (100 00.), heating equimolar quantities. of hydroquinone and 10 N aqueous methylamin for 20 hours at 220250 degrees, but the yield of the metol basewas very small and much tarry material resulted. This result Was thought to be due to a, catalytic action of theiron so the next-heats were carried out in glass. However. later experiments would seem to indicate that the iron has no-ill eflect. L

Twenty grams of hydroquinone and 22 cc. of. 10 N aqueous methylamin were introduced into each of six bomb tubes, an evolution of heat taking place when the two were .each 100 cc. of water.

mixed, due probably to the formation of the methylalmnonium salt of hydroquinone since the solution of hydroquinone alone in water is endother'mal The tubes were then sealed and placed in an oil bomb furnace, fitted with an Ostwald gas regulater which kept the temperature constant to within 5 degrees. The

the metol base caused by prolonged heating.

The tubes were then opened and the contents poured into sulfuric acid (1-20) containing a quantity of the acid just equivalent to the methylamin used. The mixture was then boiled to insure solution and the solution made up of 1 liter. A sample was analyzed for amino-nitrogen by the Van Slyke method, which consists in treating the sample with nitrous acid and collecting the gases evolved in a gas burette containing alkaline permanganate which absorbs all of the gases except nitrogen, the volume of which represents the quantity of unchanged primary amino-nitrogen. Van Slyke states that to obtain a complete reaction between methylamin and HNO a shaking of one hour is necessary, but it was found possible by keeping the room at 28 degrees and shaking at a constant speed for 15 minutes to obtain uniform results giving 94% of the total gas. Since merely approximate and comparative results were desired it appeared unnecessary to shake for the longer period. The solution was then extracted with ether and the ether solution evaporated to dryness and weighed. It consisted principally of such hydroquinone as had remained unchanged. The water solution was concentrated to 100 cc. and cooled in ice, and the resulting crystals collected on a Buchner funnel, washed with alcohol, dried and 'weighed. Analysis showed that they were practically pure metol. They were of a grayish color and were easily rendered pure white by recrystallizing from boiling water containing 1 g. of decolorizing charcoal for The results of the six runs are given in the following table. They show that the react-ion at 200 degrees is practically complete at the end of the third hour and that longer heating merely lowers the yield of metol and produces tarry products insoluble in a solution of sulfuric acid. The yield given does not represent the portion remaining in the 100 cc. of

mother liquor and is therefore given too low.

-Table 1.Reacti0n o h dro ui'none and meth lamin at 1 q 1! 200 degrees.

N evolved Time Ether sol. Wt. of Yield (hrs.). 12,22 material. metol. Remarks 22. 33 cc. 0 g

7. 5 1 7.55 3g. 115 31 2 gg 2g. Lower layer 47 clear, no tar. 35.....{ 0.8g 14g. 45 6 3.50 1.8g 13g 42 A little tarry matter. 2.93 15..... 1.6 More tarr matter, ofliansive 3 25 M li t t 24..... 1.2 7 25 uc arrymag ter, ether sol. material almost black.

A heat was then carried out as above but using alcoholic methylamin (7.4 N) and heating for 3 hours. No separation into layers occurred upon cooling and analysis showed that 21% of the amino-nitrogen and 25% of the hydroquinone remained and the yield of metol was 38%.

' Twenty grams of hydroquinone was next heated with two equivalents of aqueous methylamin (10 N) for 4 hours at 200 degrees. No layers separated upon cooling and there remained 53% of the methylamin used, equal to a disappearance of 91% of one equivalent of the amin. The yield of metol was 19.8 g. and 3 g. more were recovered from the mother liquor making a total yield of 73 75-. The crystals were almost white.

A still lower temperature than 200 degrees was now tried, equivalent quantities of hydroquinone and 10 N aqueous methylamln being heated for 20 hours at a temperature of 120-160 degrees. Two layers separated upon cooling, the upper one being 16% of the total height of the fluids in the tube, the lower being of a much lighter color than the corresponding layers obtained at 200 degrees. The disappearance of ammo mtrogen was 82%, and 28% of the hydroquinone was recovered unchanged. The yield of what .is known commercially as metol was 7 g from 10 g. of hydroquinone (45%) or a yield of 62% on the basis of hydroquinone actually utilized. This does not include the quantity of metol remaining in the mother liquor.

In a similar experiment using 7 .4 N alcoholic methylamin the loss in amino N was only 60% and the material was not further investigated.

Equivalent. quantities of hydroquinone and 10 N aqueous methylamin were heated for 6 days in the steam-bath. A decrease of 24% in the amino-nitrogen was shown, which would indicate that the reaction begins even at this temperature.

A heat was carried out at 200 degrees add 'limc Pressure (Minutes). (Atmospheres).

This result would suggest that a pressure gage reading could be used to follow the reaction. 1

Another heat was carried out at 150 degrees with the following results:

That the product made from. hydroquinone and methylamin is identical with metol was further shown by making the benzoyl derivatives of the two, both of which melted at 17 4 degrees, and a mixture of the two melted at the same temperature. The

method of synthesis is, however, suflicient' proof of the structure.

The following characteristics of N-methyl- 'p-amido phenol sulfate, hitherto unpublished, may be of interest:

The compound begins to char at 245 degrees and melts with decomposition at 250260 degrees. One part dissolves in six parts of boiling water and in twenty parts of water at 25 degrees. It crystallizes from water in colorless needles which under the microscope appear as six-sided prisms having roof-like ends. \Vhen a solution of mercuric acetate is added to a solution of the salt the solution assumes an intense purple coloration. This color comes gradually, about three minutes elapsing before the full color is developed. In solutions of metol stronger than 11000 the production of the color is accompanied by the precipitation of beautiful scales which were found to be mercurous acetate, and the color in this concentration is best described as being very similar to that of ordinary grape juice. The formation of mercurous acetate would indicate that the color is an oxidation product. The color observed by Clark upon treating metol with a solution of ferric chlorid, is no doubt also produced by oxidation, but the color caused by mercuric acetate is many times more intense.

Hydroquinone and the salts of p-amino phenol give no color at all when treated with mercuric acetate, and is developed by a very small quantity of 'metol (a solution 110000 giving a very good intensity) this reaction might be used to estimate the compound colorimetrically and some experiments with the Schreiner colorimeter gave promising results. Amidol (C6H3-"OH (NH2)2 1, 2, 4) gives a somewhat similar color, but this is changed to pink on the addition of acetic acid while the purple color produced by metol remains unchanged under similar treatment.

It will thus be seen that my process has the following advantages over processes heretofore known for the manufacture of N-methyl p-amino phenol or its sulfate.

First. A lower temperature is employed,

which involves a smaller expenditure of heat and results in a much better yield of the desired product, since at the high temperature the production of tarry material is very great.

Second. A very much lower pressure is required, which permits the use of lighter and cheaper machinery than if higher pressure were used.

since the color I Third. A shorter heating period is used. 7

uct is produced by either a lower temperature (lower pressure) or a shorter period of heart, as set forth above, or by a combination of lower temperature (lower pressure) and shorter heating period.

Fifth. A much better yield of the product is obtained by using a greater chemical proportion of methylamin than -hydroquinone.

Having described my invention, what I claim is:

1. The process of manufacturing N-methyl p-a ino phenol by heating together hydroqui one and methylamin at a temperature of 150 degrees for a period of five hours.

2. The process of manufacturing N-methyl p-a-mino phenol by heating a mixture of hydroquinone and methylamin at a temperature of 200 degrees for a period of two hours.

3. The process of manufacturing N -methyl p-amino phenol by heating a mixture of hydroquinone and methylamin at a temperature between 150 and 200 degrees for a period between two and five hours.

4. The process of manufacturing N methyl p-amino phenol by heating together hydroquinone with an excess of methylamin at a temperature of 150 degrees for a period of five hours.

5. The process of manufacturing N-methyl p-amino phenol by heating together hydroquinone with an excess of methylamin at a temperature of 200 degrees for a period of two hours.

'6. The process of manufacturing N-methyl p-amino phenol by heating together hydroquinone with an excess of methylamin ,at a temperature between 150 degrees and 200 degrees for a period between two and five hours. 1

In testimony whereof, I afiix my signature in the presence of subscribed witnesses.

ROLLA N. HARGER. 

